Structures that are used very commonly in architecture in civil engineering works such as dams, nuclear power plants, bridges, tunnels, etc., as well as generally in fields related to mechanics, generally undergo mechanical stresses during their construction and throughout their service life. The application of these stresses causes deformations within the volume of these structures which can result in altering their mechanical properties. Autogenous shrinkage, namely shrinkage that originates inside the body of the structure, of the material composing the structure is particularly problematic during creation of the structure, for example during creation of a structure made of cementitious matrices with a low water/cement ratio, and is a cause of premature cracking of the material. Indeed, the capillary pressure generated by self-desiccation can reach very high values (several megapascals (MPa) according to Hua et al., 1995). Several studies have shown that the endogenous shrinkage that occurs during the first day of the solidification phase represents a very significant share of the endogenous deformations of the material over the long term: after the first twenty-four hours, the endogenous deformation can reach over 40% (Baroghel-Bouny and Kheirbek, 2001), or for some high-performance concretes, more than 80% (Lee et al., 2003), of the deformation measured after a year of maturation in endogenous conditions.
To monitor the quality of these structures, it is necessary to be able to measure the evolution of the deformations that occur in these structures during the first few days, between one and four days and preferably during the first three days, of the transition of the material from liquid phase (paste) to solid phase.
The evolution of the deformations of structures and the estimation of the stresses acting on them can be monitored by devices placed on the outer surface of the structures, such as visual indicators for deformations or mechanical sensors sensitive to deformation at the surface of these structures (FR2855210). Deformation measurements within a structure can be estimated by integrating within the volume of the structure a uniaxial sensor or “measurement fiber” such as an optical fiber (WO2006127034). However, at best these methods only allow estimating an average, along the axis of the sensor, of stress or deformation components exerted in a fiber placed in the monitored volume. Finally, direct integration of a sensor into the monitored structure can result in weakening said structure, due to the change in distribution of stresses in the volume of the structure near the sensor, the particular shape of the sensor possibly resulting in local concentrations of stresses conducive to crack initiation around the sensor.
The present invention aims to improve the quality and reliability of the measurement of endogenous deformations occurring locally within a structure. In particular, the present invention aims to improve the quality and reliability of the measurement of endogenous deformations occurring locally within a structure during solidification of the structure.